The present invention relates to a method and an apparatus for treatment of fluids. Fluids will in this context be understood as gases and liquid media as well as suspensions and emulsions.
In recent years, ever greater demands have been placed on the environment wherever man has been present. There are many reasons for this. One is that modem man""s mobility between different geographical areas means that pathogens find fertile breeding ground for development of extremely virulent strains. These can give rise to serious diseases for which there are as yet no cures.
In hospitals, pathogens can be transmitted from one patient to other personsxe2x80x94both patients and nursing staffxe2x80x94and these pathogens are transmitted further by direct contact or indirectly via instruments, clothes, food or the like. Hospital textiles are contaminated to a greater or lesser extent with pathogens. One problem is that the washing methods are not completely satisfactory as regards removal of pathogens from hospital textiles. In addition, there is a need for better and simpler methods for sterilization, on the one hand of sensitive equipment such as, for example, endoscopy instruments and catheters which do not tolerate conventional sterilization methods, and, on the other hand, in operations where instruments need to be sterilized directly and quickly as they may have become contaminated during surgery (the surgeon may, for example, drop special instruments, implants and the like).
Other environments where pathogens and other types of pollution are spread and which often have problems with poor air are schools, day nurseries, food shops, kitchens, ship cabins, industrial premises and the like, especially in poorly ventilated premises. A further problem area is xe2x80x9csick housesxe2x80x9d with, for example, radon, mould, hexamine and the like, as well as premises which are being painted, papered, floored, etc.
Water is another area where ever greater demands are being placed both on purity and on minimizing the environmental pollution when treating drinking water and waste water.
These media, and media contaminated in other ways, have created considerable unrest and the need for effective decontamination processes.
A number of proposals for dealing with the abovementioned problems have been put forward during the years, such as better ventilation, various types of filters and chemicals for purification of air and water. Since chlorine itself is a burden on the environment, methods have been developed in several countries for purifying water with ozone (O3) in drinking water installations and bathing facilities, and also ozone dissolved in water for cleaning, disinfection and sterilization of articles. The reaction capacity of ozone (2.07 V electrochemical oxidation potential) is ascribed to the fact that it is a powerful oxidant. The high chemical reactivity is coupled with the unstable electron configuration which seeks electrons from other molecules, which thus means that free radicals are formed. In this process, the ozone molecule is broken down. By means of its oxidizing effect, the ozone acts rapidly on certain inorganic and organic substances. Its oxidizing effect on certain hydrocarbons, saccharides, pesticides, etc., can mean that ozone is a good choice of chemical in certain processes. A combination of ozone, oxygen, hydroperoxide and UV radiation means that the reaction proceeds much more quickly and more efficiently by virtue of the generation of more free radicals.
The inactivation of microorganisms with the aid of ozone and radicals is considered as an oxidation reaction. The membrane of the microorganism is the first to be attacked. Within the membrane/cell wall, the ozone and the radicals destroy nuclear material inside the cell/virus/spore. The inactivation reaction in the case of most microorganisms occurs within minutes, depending on the ozone dose and the amount of free radicals which are formed.
In most cases, ozone is used in the form of ozone water for
removing or reducing chemicals, dyes, heavy metals, odour, and destroying pathogens in water-purification works,
removing algae, fungus, deposits, and for reducing the use of chemicals in water-cooling systems and heat exchangers,
treating water in pools, aquariums and fish farms,
sterilizing bottles and jars which are used in the beverage and food industry.
Despite its solubility in cold water, ozone is broken down (=consumed) quickly, as is the case in air, which gives a great many different radicals and more or less stable by-products such as aldehydes, bromate and carboxylic acids. The degree of breaking down depends on the pH, the substance which is exposed and the temperature. Certain substances are broken down easily by the ozone. However, the majority of substances and molecules are oxidized more efficiently by free radicals which are formed by ozone and the media treated by ozone. Certain free radicals have a higher electrochemical oxidation potential than ozone (2.8 V for hydroxyl radical and 2.42 for oxygen (singlet)). Examples of common oxidants which can be formed are hydroxyl radicals (HOxe2x88x92), peroxyl radicals (RO2xe2x88x92), (singlet) oxygen (1O2), diradicals (Rxe2x88x92xe2x80x94Oxe2x88x92) and alkoxy radicals (ROxe2x88x92).
Oxidation of organic molecules is best understood on the basis of the two similar paths for reactions of HOxe2x88x92, ROxe2x88x92, RO2xe2x88x92 and 1O2 radicals. Most organic chemicals which are mixed with air as gases are oxidized by HOxe2x88x92 radicals. Aliphatic molecules give RO2xe2x88x92 radicals which can undergo various reactions, the most significant of which is the conversion to an alkoxyl radical (ROxe2x88x92) via NO. Reactions of ROxe2x88x92 radicals are rapid and produce new carbon radicals by cleaving or by intramolecular transfer of H atoms. A reaction cycle of intramolecular transfer of H atoms, formation of a new RO2xe2x88x92 radical, conversion to the corresponding ROxe2x88x92 radical and, finally, a further intramolecular reaction can lead to highly oxidized carbon chains.
Aromatic molecules oxidize quickly with HOxe2x88x92 radicals, which forms carbon radicals and phenols. Singlet oxygen (1O2) is important for oxidizing a great many organic chemicals, including amino acids, mercaptans, sulphides and polycyclic aromatic hydrocarbons. These too are rapid oxidation processes.
Consequently, ozone reacts with contaminants via two essential pathways. It can react directly, as molecular ozone (O3), by reactions which are selective. In general, activated compounds (phenol, resorcinol, salicylate), olefins and simple amines are expected to react with molecular ozone, as are certain microorganisms.
Alternatively, ozone can react with contaminants via an indirect route, in which the free radicals, which are produced by decomposition of ozone and by reactions, serve as oxidants. These indirect reactions of the radical type are rapid and non-selective.
Organic contaminants which react slowly with molecular ozone, such as aliphatic acids, aldehydes, ketones and aromatic hydrocarbons, react to a greater extent via the non-selective radical route. Thus, the conditions which break down ozone, such as UV radiation, favour indirect and non-selective reactions where the free radicals formed are strong oxidants. In the case of air, the radical route has a predominant role in most oxidation processes. Even in situations where the first oxidation reaction between the ozone and contaminants takes place via the direct route, radicals are generated so that the subsequent oxidation takes place effectively and rapidly by means of radical reaction processes.
Since the radicals are non-selective, they can oxidize all reduced substances and are not limited to specific classes of contaminants, as is the case with molecular ozone.
As has been mentioned, UV radiation favours a rapid decomposition of ozone with subsequent formation of radicals. In those cases where contaminants absorb UV radiation (for example, tetrachloroethylene), direct photolysis of the pollutant contributes to the degree of oxidation.
In many apparatuses, ozone is generated by corona discharges. When a 6-7 eV electron interacts with an oxygen molecule (O2), dissociation takes place. The oxygen atoms (O+O) which are formed are immediately combined with oxygen molecules to form ozone (O3).
It is also known that UV radiation with a wavelength of approximately 183 nm gives rise to ozone in air. However, it is difficult to make such lamps adequately effective for production of ozone in the large quantities which may be needed in many cases.
A number of trials on purifying air with ozone have been carried out, such as described, for example, in the patent U.S. Pat. No. 5,186,907. The patent describes an apparatus for treatment of organic waste gases which contain toxic components as organic solvents. The gases are sucked into an enclosure by a fan and are initially exposed in the said enclosure to a first oxidizing member, for example a UV lamp, which causes oxygen in the air to form ozone. The oxidizing effect of the ozone means that most of the organic solution forms peroxide. The peroxide is then irradiated by a second oxidizing member, in this case a UV lamp which emits radiation at a wavelength of 365 nm, so that the peroxide is broken down almost completely to carbon dioxide, water and inorganic gas components by oxidation. At the same time, those parts of the organic gas which were not oxidized by the first oxidizing member and the ozone will be oxidized and broken down by the second oxidizing member.
The apparatus in accordance with the above is targeted at organic solvents such as isopropyl alcohol, where the first oxidizing member converts the solution to peroxide, which is then oxidized by the radiation from a UV lamp at a wavelength of 365 nm. This apparatus has a narrow scope of application, specifically for treatment of certain defined organic solvents.
In the patent U.S. Pat. No. 5,260,036, a method of photochemically oxidizing gaseous halogenic organic compounds is disclosed. According to the patent, the compounds are exposed to UV light to oxidize them into gaseous oxidation products and reacting the gaseous oxidation products with a surface inside an oxidation chamber, where the surface a material which is chemically reactive with the gaseous oxidation products in order to produce solid reaction products incorporated in side walls of the chamber. This chemically sorbant internal surface material has a life of 1-3 months.
It is evident from what has been described above that ozone can be used to good effect for purifying, disinfecting and sterilizing within certain areas and in the case of certain substances. The use of ozone for the purpose of obtaining free radicals therefrom should, however, considerably increase the efficiency, the scope of application and the substances which can be rendered safe. This procedure has not until now been used effectively.
The object of the invention is to tackle the abovementioned set of problems with purification and disinfection of contaminated media such as air, water and solid articles, and also disinfection and sterilization of articles in a more efficient manner than has been possible with previous methods and apparatuses. This is achieved by means of a procedure and apparatus according to the characterizing clauses of Patent Claim 1 and Patent Claim 5.